A punch is used in conjunction with a punch driver to punch holes in sheet metal, for example in the walls of electrical cabinets, aluminum, fiberglass and plastic.
Generally, when a hole is to be punched in an electrical cabinet, a small hole is first drilled in the wall of the electrical cabinet. A first end of a draw stud is threaded into a ram of a hydraulic punch driver. A second end of the draw stud is inserted through a punching die and then through the drilled hole, the draw stud having a diameter that is less than the diameter of the drilled hole. A knockout punch is threaded onto the second end of the draw stud on the opposite side of the electrical cabinet than is the punching die and the hydraulic punch driver.
An operator actuates a hand pump of the hydraulic punch driver. When the hand pump of the hydraulic punch driver is actuated, hydraulic fluid forces the ram to pull the draw stud. The draw stud, in turn, pulls the knockout punch through the electrical cabinet into the die such that the desired hole size is punched.
Hydraulic systems (hand pump, hose, and ram) that electricians use to punch holes in electrical cabinets have a rated capacity of 11 Ton (22,000 pounds force). Punching large holes (up to 4.5″ diameter) in 10 gage (0.134 inch thick) stainless steel with a conventional 4-point punch requires 12-15 Tons (24,000 to 30,000 pounds force).
A disadvantage of prior art punches is that they commonly have surfaces which cannot be easily machined with standard cutting tools, such that custom formed tools or broaches are required to cut the punch profile.
In addition, higher punching force are required if the cutting edge of the punch is “too dull” (neutral or negative cut edge geometry). Reduced punch durability occurs if the punch cutting edge is too “sharp” (positive cut edge geometry). A less ideal punch/die clearance leads to a higher frequency of “chipping” the punch or die cutting edge due to misalignment of the punch and die.
With regard to cutting a hole in 10 gage stainless steel, such a hole can be cut with great physical effort and high tool wear cost. A 4″ conduit hole can be made in 10 gage stainless steel using a carbide hole cutter, or possibly a carbide grit hole saw, reciprocating saw, or saber saw. All these methods, however, are labor intensive and may wear out several tools in order to make just one hole.
A punch assembly is provided herein which provides improvements to existing punches and which overcomes the disadvantages presented by the prior art. Other features and advantages will become apparent upon a reading of the attached specification, in combination with a study of the drawings.